Modeling the Normal Spectral Emissivity of Red Copper T2 at 800–1,100 K During the Growth of Oxide Layer

Abstract

This paper strives to model the normal spectral emissivity of red copper T2 during the growth of oxide layer at 800–1,100 K. For this reason, the normal spectral emissivity of red copper T2 specimens is evaluated at the sixteen definite temperatures during a 6-h heating period. In experiment, the normal radiance is measured using an InGaAs photodiode detector at 1.5 μm, which is perpendicular to the surface of specimens as accurately as possible. The temperature of specimen surface is obtained by averaging the two platinum–rhodium thermocouples, which are welded symmetrically and tightly in the front surface of specimens near the measuring area viewed by the detector. The strong oscillation of normal spectral emissivity occurs only during the initial heating period at each definite temperature, which has been affirmed to be connected with the thickness of oxide layer on the specimen surface. The interference effect between the radiation coming from the oxide layer on the specimen surface and the radiation stemming from the substrate is discussed, which is responsible to the strong oscillations of normal spectral emissivity. The uncertainty of normal spectral emissivity contributed only by the surface oxidization is estimated to be 3.3–10.0 %, and the corresponding uncertainty of temperature is estimated to be about 3.2–10.0 K. The analytical models between the normal spectral emissivity and the heating time are evaluated in detail. A simple functional form with the exponential and logarithmic functions has been found to reproduce well the variation of normal spectral emissivity with the heating time, including the fundamental reproduction of strong oscillation occurring during the initial heating period.